Switching converters are applied to convert an input power source to a desired power source so as to power electrical devices properly. In order to meet the input voltage requirement of the electrical devices, a voltage provided by the switching converter should be limited in a preset range. Thus, a voltage detecting circuit is needed to make sure the voltage provided by the switching converter is suitable. FIG. 1 schematically shows a prior art switching converter, i.e., Flyback converter with a voltage detecting circuit. As shown in FIG. 1, the voltage detecting circuit comprises an optocoupler D0, a third winding Lt, diodes D2 and D3, a capacitor C3, and resistors R10, R12, and R13. The optocoupler D0 detects an output voltage Vo of the Flyback converter, and the third winding Lt feeds back the output voltage Vo to a feedback pin FB of a control chip 101 of the Flyback converter. The voltage detecting circuit for detecting the output voltage Vo in FIG. 1 is very complicated, and many components like the optocoupler D0, the third winding Lt and so on are needed, which increases the cost.